Association between characteristics of nursing teams and patients' aggressive behavior in closed psychiatric wards

Abstract Purpose Estimate the effect of nursing, shift, and patient characteristics on patients' aggression. Design and Methods Follow‐up study on a closed psychiatric ward was performed to estimate the effect of nursing team characteristics and patient characteristics on the incidence of aggression. Findings The incidence of aggression (n = 802 in sample) was lower in teams with >75% male nurses. Teams scoring high on extraversion experienced more verbal aggression and teams scoring high on neuroticism experienced more physical aggression. Younger patients and/or involuntarily admitted patients were more frequently aggressive. Practice Implications These findings could stimulate support for nurses to prevent aggression.

Aggressive behavior varies in manifestation, ranging from verbal aggression (e.g., shouting and threatening) to physical assault (Renwick et al., 2016). Nurses in closed psychiatric wards are at high risk of encountering aggressive behavior; more than half of them are victims of assault by patients during their career (Jang et al., 2021;Odes et al., 2021;Spector et al., 2014). Aggressive behavior toward nurses on psychiatric wards causes stress, anxiety, and injuries (Hilton et al., 2021;Needham et al., 2005). Subsequently, aggressive behavior is the main reason for nurses to use coercive measures (e.g., seclusion or restraint) (Cowman et al., 2017;Laukkanen et al., 2019).
Coercive measures are also associated with serious adverse events (Funayama & Takata, 2019;Kersting et al., 2019). If we gain more insight into factors causing aggressive behavior, we can use it to reduce or prevent aggressive behavior.
Several meta-analyses investigated which patient characteristics influence the incidence of aggressive behavior, such as male sex, young age, and/or involuntary admission (Iozzino et al., 2015;Weltens et al., 2021). Although highly relevant, concentrating solely on patient characteristics to assess the risk of aggressive behavior is a one-sided strategy. The role of nursing characteristics can provide further insight in the risk or aggressive behavior (Ayhan et al., 2021;Lamanna et al., 2016;Weltens et al., 2021). Salzmann-Erikson and Yifter (2019) found that nurses with longer employment encountered less aggressive patient behavior during their shift. They also reported that most aggressive incidents occurred in the evening shift (Salzmann-Erikson & Yifter, 2019). Schlup et al. (2021) reported a lower self-reported incidence of aggression with more experienced nurses. Başoğul et al. (2019) found that nurses with stronger needs for positive interaction with others reported more verbal aggression (Başoğul et al., 2019). While most authors reported results of verbal and physical aggression together, others analyzed verbal and physical aggression separately and found (small) differences in risk factors. Bowers, Allan et al. (2009) reported an association between the presence of student nurses and verbally aggressive patient behavior, but not with physical aggression. Başoğul et al. (2019) found that awareness of their own emotions by nurses was associated with less physical aggressive patient behavior. Besides factors of individual nurses, the literature describes several organizational factors that influence aggressive behavior of patients in mental health care, such as organizational justice, collaboration between staff, ward atmosphere, work functioning, and leadership (Bowers, 2009;Giménez Lozano et al., 2021;Magnavita et al., 2020;Pekurinen et al., 2017).
In summary, previous studies found several patient and nurse characteristics being associated with aggressive behavior of patients.
However, most studies measured the association between individual nurse characteristics and their self-reported experience with aggressive behavior. We propose to take into account nursing team, shift, and patient characteristics to estimate their effect on more reliably measured incidents of aggressive behavior. In the current study, we addressed the following questions: (1) Which nursing team (e.g., personality traits, sex, and education), shift (e.g., patient-staff ratio), and patient characteristics (e.g., sex and diagnosis) are associated with the incidence of aggressive patient behavior in closed psychiatric wards?
(2) Do associations differ between verbal aggression and physical aggression? 2 | METHODS

| Design
We performed a prospective 2-year follow-up study on a closed psychiatric ward.

| Participants and setting
Our study was performed at the closed psychiatric admission ward of Amsterdam University Medical Centers (location Academic Medical Center) in the Netherlands. The ward is responsible for the involuntary admissions from densely populated, multicultural neighborhoods in Amsterdam. The ward had 12 patient rooms and two seclusion rooms, which serves as the last-resort coercive measure in case of dangerous situations due to aggressive behavior. We included all patients admitted to the ward between January 1, 2013 and December 31, 2014. The majority of admissions were involuntary and related to acute psychiatric crises leading to danger, according to the local Mental Health Act. Nurses worked in three shifts with four registered nurses on 12 patients between 7:30 a.m. and 11:00 p.m.
(day shift and evening shift) and two nurses at night. Student nurses work on a supernumerary basis.

| Variables and measurements
We gathered nurses' baseline data with a case record form. Data collection on nurses consisted of sex, age, body mass index (BMI), physical stature, registration as a nurse (RN), highest education, fulltime or part-time employment, duration of employment, and years of experience in mental health care. We defined physical stature as a nurse's subjective physical appearance, estimated on a 5-point scale (very small, small, average, large, and very large). Three assessors independently rated stature; the observer agreement was moderate, Fleiss κ = 0.43.
Psychological measurements consisted of the Big Five personality traits (neuroticism, extraversion, openness, agreeableness, and conscientiousness) and a general feeling of safety during their work.
We assessed personality traits using an online self-report 60-item Neuroticism Extraversion Openness Five-Factor Inventory 3 (NEO-FFI-3) (McCrae et al., 2005). This instrument has adequate to good psychometric properties in patient groups and the general population (Hoekstra & De Fruyt, 2014;McCrae et al., 2005). Despite extensive literature research, we were unable to obtain a validated questionnaire to measure nurses' feelings of safety in psychiatric wards. Therefore, we used four questions with a 5-point Likert scale about whether nurses generally felt safe in their organization, on their ward, with their colleagues, and with their manager.
We gathered baseline data on patients within a week after the start of their first admission to the ward during the study period, using the electronic health records. Patients' baseline data consisted of sex, age, length of admission, involuntariness of admission, primary and secondary diagnosis, whether the admission occurred after an aggressive incident, and current psychiatric status (based on the Health of Nation Outcome Scale [Wing et al., 1998] and Global Assessment of Functioning [Jones et al., 1995]).
We collected shift data in all shifts during the data collection period, that is, three times a day (day afternoon and night shift). To prevent bias due to underreporting of aggressive incidents, we screened daily nursing reports. The first author read all nursing reports for the admitted patients during the study period to find possible aggressive incidents. We performed outcome measurements for every patient during the entire study period using the Staff Observation Aggression Scale-Revised (SOAS-R) (Nijman et al., 1999). Variables and measurements are described in detail in

| Ethical considerations
Patients on closed psychiatric wards are a vulnerable population and researchers should be meticulous in protecting their rights (Helmchen, 2010). We requested the Medical Ethics Review Committee of our institution for approval according to the Medical Research Involving Human Subject Act (WMO). The committee concluded that formal approval of current study was not obligatory, as our study observed routine patient care and did not subject patients to additional procedures, behavioral rules or diagnostic testing (reference number A1-12 17 0320). Because of the absence of impact on patients and the importance of our study aims, we were allowed not to seek active consent to re-use patients' data for this study, according to the exception grounds of article 24 of the GDPR Implementation Act. To protect patients' privacy, only members of clinical staff performed data collection from the electronic health record. The current study used anonymized data in all analyses. Staff members were asked to participate on a voluntary basis and gave permission to use of their data in the analysis. Staff members were free to refuse participation and researchers did not communicate the (non)participation.

| Statistical analysis
In this study, 98 different nurses, over the 2 years of follow-up, formed 1299 different team compositions during 2190 shifts (three shifts during 730 days). Patients encountered many teams and many different nurses during their admission(s). Statistical literature refers to this nonhierarchical structure as cross-classified data (Fielding & Goldstein, 2006). Cross-classification signifies that our data do not have a simple hierarchical structure in which shift teams have fixed compositions of nurses and each patient receives care from a single nurse during the entire admission.
We analyzed the data by constructing a cross-classified multilevel logistic regression model with occurrences of aggressive behavior as the dependent variable and nursing team, shift, and patient characteristics as independent variables. Team variables consisted of the mean score of the nurses present in a particular team, such as sex (two males and two females would yield 0.5), education, and personality traits. To improve the stability of the model, we categorized numerical variables using four categories for demographic variables and three categories (cutoffs of the 17th and 83rd centile values) for psychological categories, using the lowest category as a reference category. In STATA SE, version 15, we ran the runmlwin command to use MLwiN, version 3.02. We obtained starting values for the Markov Chain Monte Carlo analyses using penalized quasi-likelihood estimates (PQL2). The burn-in value was 2000 and the number of chains run was 20,000. We report odds ratios and their corresponding 95% credible intervals (95% CrI). We

| Participants
For a summary of baseline characteristics of the nursing staff, we would like to refer to Table 1. In total, 98 nurses worked at least one shift during the study period. The majority were females (n = 60) and the mean age was 36 years (range 18-61).
Incomplete case record forms (n = 7) were the main cause of missing data. Table 2 contains the psychological trait scores of the nurses.
Internal consistency was acceptable for neuroticism, extraversion, conscientiousness, and the general feeling of safety, however, low for openness and agreeableness. This is in line with findings in several samples in the population (Hoekstra & De Fruyt, 2014).
Average team scores of the nurses were higher on extraversion and openness and lower on neuroticism, compared to reference categories in the general population (Hoekstra & De Fruyt, 2014).
Thirty-six nurses did not respond or refused participation in the psychological questionnaire. Most non-responders (n = 33; 92%) were temporary staff members, who worked during fewer shifts than regular staff.

| Outcomes
Tables 4a and 4b contain the observations of aggressive behavior.
We documented 802 aggressive incidents during the data collection period. We divided aggressive incidents into verbal aggression (i.e., "verbal aggression" and "physically threatening" in the SOAS-R) and physical aggression (i.e., "physical violence towards goods," physical violence towards nursing staff," and "physical violence towards fellow patients" in the SOAS-R). We documented 438 incidents of verbal aggression only and 364 incidents of physical aggression.

| Main results
In multilevel modeling, we observed high collinearity between nurses' experience in mental health care and nurses' age. We dropped age from the final analysis since we deemed experience a more important concept than age for our purpose. We dropped the following nursing  (2019) found evidence in their review for an association of several diagnostic categories with aggressive behavior, such as psychotic disorders, bipolar disorder and personality disorders. Equivocalness in findings of diagnostic categories suggests that these findings are highly sample-dependent.
We found an association between all female nurses in a team and increased odds of aggressive behavior. Because of the equivocalness of this characteristic in other studies, we are cautious in assuming a causal relationship (Odes et al., 2021). We found associations between higher nursing teams' mean of personality trait extraversion and more verbal aggression and, although less strong, higher nursing team's mean of personality trait neuroticism and more physical aggression. Extravert individuals are characterized by enthusiasm and they can be perceived as dominant in groups of people (McCrae et al., 2005). This may indicate that extravert staff members can be a trigger for patients' aggression. Another possible explanation is that teams with high levels of extraversion actively seek interaction with patients and therefore encounter more verbal aggression but deescalate this before exacerbation into physical violence. Neurotic persons are characterized by emotional instability and are sensitive to stress (McCrae et al., 2005). A possible explanation for the association with physical aggression could be a tendency of teams with high levels of neuroticism to be anxious to intervene early in the development of aggression and therefore may encounter more physical aggression. There is little evidence on the association between staff personality trait and patients' aggressive behavior. Bilgin (2009)  found an association between sociotropic personality characteristics and verbal aggression. Sociotropic individuals have good empathy skills and interest in helping others during interpersonal interaction and may be comparable to the agreeableness personality trait, which we found to be not associated with aggressive behavior. However, extrapolation of the personality traits we measured to other models of psychological characteristics is highly speculative. Therefore, we need to be cautious in comparing our findings with results found with other models. Lastly, we found a nonsignificant trend toward a higher team scores of feelings of safety and more verbal aggressive behavior. A possible explanation for this finding, apart from chance, is that teams that generally feel safer tend to seek interaction with patients and therefore encounter more verbal aggression. Future research could evaluate the effects of feelings of safety of staff members on the incidence of aggressive behavior.
Our study has several limitations. We decided to exclude data on patient's current clinical state because of poor data quality.
Therefore, we were unable to account for the influence of severity of the disorder on the risk of aggressive behavior. Furthermore, nurses were aware of the fact that we performed a study about aggressive behavior. We cannot rule out that this influenced their behavior or their reporting of aggressive behavior, although we used regular daily nursing reports as a primary data source. We analyzed nursing characteristics at the team level. The cross-classified data structure limited the possibility to analyze the effect at the level of individual nurses, due to nonconvergence of the statistical model when adding another level. This prevented us from analyzing the influence of individual characteristics of nurses. Due to the complexity of the statistical model, we were not able to analyse interaction variables between patient and team characteristics. This study was conducted in the Netherlands, which possibly limits the generalizability of our findings to other parts of the world. Lastly, this was a monocentric study, which could also limit the generalizability of our findings.

| IMPLICATIONS FOR NURSING PRACTICE
The reported associations may raise nurses' awareness about factors that may increase the probability of aggressive behavior in patients.
Our findings suggest that nursing teams with extrovert personalities are more at risk to encounter patient verbal aggression than teams with more introvert nurses are. This might imply that an interaction strategy with low expressed emotions diminishes the risk of verbal aggression. The association between a neurotic personality structure and physical aggression is a new finding (based on a nonsignificant p value) and requires replication. Anxious or controlling behavior of nurses might not protect against aggression, perhaps because nurses who feel safe reach out to patients earlier in the development of aggressive behavior. These findings could serve as a starting point for further qualitative (e.g., phenomenological analysis or participative observation of patient-staff interaction) and quantitative research on nurses' personality traits in relation to the patient outcomes. We deem it inappropriate to use current findings for selecting staff members. However, it generates possibly clinically relevant hypotheses concerning the influence of personality traits on aggressive behavior. For instance, improving the insight of nurses in their own personality traits could serve as a starting point for training and development of nurses' interactional skills. Ultimately, this may lead to the development of preventive interventions.

ACKNOWLEDGMENTS
The authors thank the nurses of the psychiatric closed admission ward of Amsterdam UMC, location Academic Medical Center, and in particular, Sascha da Silva Curiel and Joey Remmers, for their support in this study. No external or intramural funding was received.

CONFLICTS OF INTEREST
The authors declare no conflicts of interest.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

Medical Ethics Review Board of the Academic Medical Center in
Amsterdam, the Netherlands (reference number A1 -12 17 0320).